Cannabis being such a young industry and all, it wasn’t until 2011 that someone came up with a hard number on just how much energy it takes up. According to University of California researcher Evan Mills, that number was one. 1 percent of all energy in the country, he tabulated, was consumed by indoor cannabis grow houses.

And that was in 2011, before a single state had legal marijuana. In the last six years, eight states (and D.C.) have legalized recreational weed while another 13 okayed medical marijuana. So, you know, it’s probably time for a new study, but jeez, that’s a lot of power.

How do these little weed plants suck up all that juice? Well, a lot of different ways. To grow weed indoors at maximum efficiency, you need very hot lights, very cold air conditioning to make sure they don’t wither and die, an irrigation system, and a dehumidifier and fans to keep the air dry but still circulating, as pointed out in a recent Guardian article. That’s without even adding the energy used in transportation or extraction techniques.

But the biggest energy-suck by far (about 50 percent) are lights. LED lights, which might save some on electricity, are not seen as efficient or even effective by many growers. Paul Isenbergh, the owner of three marijuana cultivation warehouses in Denver, told the Guardian that he pays a monthly electricity bill of at least $4,000.

“We are consuming a lot of energy compared to what we would with LED lights,” he said.  “We tried LED but we couldn’t get the right yield from the plants. And this is a weight game. The LEDs just don’t have the horsepower.”

This all creates a little bit of a paradox for hippies who like to think green in both senses of the word. Denver has become a Mecca for the cannabis industry partially because of its hippy-ish sensibilities. But now the weed industry itself may threaten the city’s environmental goals. Denver signed up to meet Paris climate agreement goals and intends to cut its greenhouse gas emissions 80 percent by the year 2050. But the city is actually increasing its electricity use by 1 percent per year, with nearly half of that due to cannabis grow houses.

Be that as it may, Evan Mills thinks that legalizing cannabis is the only way to stop the regulate its energy consumption, as he argued in an op ed last year. “Until then, some of the nation’s hard-earned progress towards climate change solutions is on the chopping block as regulators continue to ignore this industry’s mushrooming carbon footprint,” he wrote.

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